This invention relates to improved methods of manufacturing or processing contact lens materials employing a supercritical fluid.
Polymerized contact lens materials must not only have sufficient optical clarity, but also must be suitable for contact with the eye for extended periods. The contact lenses made from such materials must be sufficiently hydrophilic at the lens surface to properly "wet". Wetting is the characteristic understood to relate to the contact lens' ability to be lubricated by the eye's natural tears so that the lens may move freely over the eye during its use. This freedom of movement over the eye keeps the lens from adhering to the eye and allows a continuous stream of tears to wash under and over the lens, resulting in maximum comfort.
The ability of a lens to properly wet and be "comfortable" in the eye is difficult to predict. Much work in the field has been directed to achieving and maintaining a hydrophilic environment or the contact lens surface. Incorporation of a variety of hydrophilic monomers into the monomer mix, as well as post-treatments such as plasma treatments have been attempted, with some success, to maintain hydrophilicity at the lens surface. However, attempts to improve and maintain adequate hydrophilicity must not compromise the other important lens characteristics, such as optical clarity. Conversely, attempts to improve or retain a high degree of optical clarity, oxygen permeability, tear strength, etc., while maintaining the proper modulus, must not adversely affect the lens' wetting capabilities.
A method of lens treatment which would not adversely affect the lens' wetting or other physical characteristics, but which could improve the lens' optical clarity would be desirable. In addition, a lens treatment which could improve the hydrophilicity of a lens, thereby eliminating or at least reducing the need for additives or post-treatment would be advantageous.
Because of certain processing limitations, most soft hydrogel contact lens production results in a molded lens which must be handled, inspected and shipped in a wet state. This processing limitation adds time and cost to the overall lens production. However, a cost-effective lens treatment which could produce a dry lens could simplify lens production and reduce the cost of lenses.
It will also be appreciated that large-scale manufacturing processes require disposal of relatively high volumes of the extraction solutions used to remove impurities and residual materials (sometimes referred to as residuals or extractables) from the lenses. In addition, various materials used as solvents provide potentially hazardous conditions to working environments due to material toxicity to humans or flammability, for example. An extraction technique using a non-toxic, preferentially recyclable extraction solvent would be desirable.